This invention pertains to a photovoltaic device having a luminescent collector with divergent surfaces and edge mounted cells, thereby changing the internal surface angle of reflection of collected light energy.
It has been proposed, in for example, APPLIED OPTICS, Volume 15, No. 10, Pages 2299-2300, October 1976, the disclosure of which is incorporated herein by reference, to convert solar radiation to electrical energy with a solar cell comprised of a planar sheet of luminescent medium with edge coupled semiconductor photocells. The collector is a sheet of material having parallel upper and lower surfaces. Solar radiation enters the collector through the upper surface. Both the upper and the bottom surface of the collector are kept free of absorptive or nonreflective substances so that internally the surfaces tend to reflect collected light energy but light energy striking either of these surfaces at the appropriate angle may escape from the collector. The collector uses luminescent dyes or materials which tend to absorb light energy in a portion of the solar spectrum. The luminescent materials reradiate the absorbed light energy at a better wavelength or energy form for conversion to electricity by a solar cell. The luminescent materials also radiate the absorbed light energy at an angle which facilitates reflection of the emitted light energy at the surfaces of the collector. Much of the useful light energy is thus trapped in the collector and propagates by successive reflections to the edges of the collector where the light energy is emitted into a photovoltaic cell.
Some of the collected light energy tends to be lost from the collector by successive reflections at the upper or lower surface. To enhance the captured properties of the collector, it has been proposed to coat or cover the bottom surface of the collector with a mirror-like coating. In addition, it has been proposed to use a protective or filtering layer ahead of the upper surface of the collector.
Luminescent materials are selected for their absorption properties, luminescent efficiency, and transmittance in the emission region. Useful light energy is lost whenever some of the light is not reflected by the upper or lower surface. It is postulated that other losses may be caused when the reradiated energy repeatedly contacts the luminescent materials, for example, as by attenuation and by conversion of useful light energy to unuseable wavelengths.